Always.
Water vapor is a common greenhouse gas found in hydrogen and oxygen. It is a naturally occurring component of the Earth's atmosphere and plays a significant role in the Earth's climate system.
There is only one element in hydrogen it's hydrogen. It's the first element in the periodic table of elements.
Hydrogen -1
natural
Some of the most common substances occurring in nature are oxygen, carbon, hydrogen, nitrogen, and calcium. These elements are essential building blocks of life and are found in various forms throughout the natural world, from the atmosphere to the Earth's crust.
Hydrogen is the most abundant element in the universe and is naturally occurring. However, most of the hydrogen used by humans is produced through industrial processes such as steam methane reforming or electrolysis of water.
Hydrogen -> Helium
nuclear fission
Tritium is the most abundant hydrogen isotope
Mineral
If you mean the most common or 'ubiquitous' element, then it is hydrogen (H).
The only pure hydrogen is found in the atmosphere as H2. Under the ground are many compounds containing hydrogen such as methane gas and water.